This invention relates to a method and apparatus for trajectory support of a surgical tool during an imaging-guided surgical operation.
Stereotactic frames play an important part in stereotactic surgery. Such frames provide a means to define a mechanical or physical trajectory in three dimensions and to support a surgical instrument or tool such that it may reach a target along the trajectory. For example, a patient may have a brain tumor which should be removed or otherwise treated. An imaging system such as computerized tomography allows the surgeon to precisely define the location of the tumor or other target. The surgeon selects an incision point on the skull of the patient and the location of the incision point is relatively precisely identified. The trajectory which the surgical tool or instrument should use is defined by the target and incision. Various stereotactic frames have been used to insure that the surgical tool follows the planned trajectory.
Since much of the activity in stereotactic surgery has been related to neurosurgery, targets are usually considered points inside a sphere, whereas incision points are selected from the surface of the sphere. Accordingly, the frames have been designed to work in a partly enclosed space such as the human head. Setting up of such an apparatus usually involves setting a number of rotational angles. For example, the most popular BRW frame uses four angles. Given the target and incision points, a special program determines four angles. As shown in FIG. 1, the prior art BRW frame 10 allows placement of a needle 12 within a patient. The frame 10 supports the needle 12 in its trajectory. Because the frame uses a non-intuitive coordinate system, a surgeon often has to repeat the calculations several times to make sure that the set of angles are correct. Further, the calculations are non-linear and the non-linearity may introduce positional errors.
Since stereotactic surgery is usually much less invasive than normal surgery, it is becoming more popular for surgical operations beyond traditional stereotactic neurosurgery. The usefulness of stereotactic surgery for operating on the neck, spine, and abdomen is becoming more appreciated. In those operations, mechanical support without a frame becomes essential. Typically, a frameless support system would use a robotic arm. Given a target and incision pair based upon a preoperatively acquired three dimensional image set and a patient space to image space registration scheme, a robot arm can be programmed to provide a trajectory support for the surgical instrument.
FIG. 2 shows a prior art robotic arm arrangement developed by Kwoh. The idea is that the patient is imaged in the same reference system as the robot arm sits. Once the target and incision pair is determined, the computer that drives the arm can be instructed to orient an end effector 14 to such a position that a surgical tool can be held by the assembly and extended to touch the target inside the patient. The arm in this design is active which, when instructed, does the orientation itself. Furthermore, it can be instructed to aim the end effector at the target as the trajectory is being changed. This feature allows the surgeon to explore all the possible incision points. This arrangement is described in more detail in Y. S. Kwoh, "A New Computerized Tomographic-Aided Robotic Stereotaxis System", Robotics Age, 7(6):17-21(1985).
A prior art passive arm is shown in FIG. 3. This design allows the surgeon to move an end effector 6 around and, correspondingly, the position of the end effector is displayed in the context of the three dimensional image acquired preoperatively. This design enables the surgeon to explore possible trajectories with total freedom. More details about this design may be obtained from Y. Kosugi et al., "An Articulated Neurosurgical Navigation System Using MRI and CT Images", IEEE Transactions on Biomedical Engineering, 35(2):147-151(1988).
Among problems with robot assisted and other frameless support systems are design complexities. Such robotic designs often leave little control to the surgeon. Furthermore, the sophisticated and expensive positional feedback systems are unnecessary when one is within imaging-guided surgical procedures. That is the imaging process can be used to track the position of the instrument or tool such that calculations of such information indirectly from the positional information of all the joints of the robot arm is not required.